/* Copyright (c) 1992-2008 The University of Tennessee.  All rights reserved.
 * See file COPYING in this directory for details. */

#ifdef __cplusplus
extern "C" {
#endif

/*  -- translated by f2c (version 19940927).
   You must link the resulting object file with the libraries:
	-lf2c -lm   (in that order)
*/

#include "f2c.h"
#include "hypre_blas.h"

/* Subroutine */ integer dtrsv_(const char *uplo,const char *trans,const char *diag, integer *n,
	doublereal *a, integer *lda, doublereal *x, integer *incx)
{


    /* System generated locals */

    /* Local variables */
    integer info;
    doublereal temp;
    integer i, j;
    extern logical lsame_(const char *,const char *);
    integer ix, jx, kx = 0;
    extern /* Subroutine */ integer xerbla_(const char *, integer *);
    logical nounit;


/*  Purpose
    =======

    DTRSV  solves one of the systems of equations

       A*x = b,   or   A'*x = b,

    where b and x are n element vectors and A is an n by n unit, or
    non-unit, upper or lower triangular matrix.

    No test for singularity or near-singularity is included in this
    routine. Such tests must be performed before calling this routine.

    Parameters
    ==========

    UPLO   - CHARACTER*1.
             On entry, UPLO specifies whether the matrix is an upper or
             lower triangular matrix as follows:

                UPLO = 'U' or 'u'   A is an upper triangular matrix.

                UPLO = 'L' or 'l'   A is a lower triangular matrix.

             Unchanged on exit.

    TRANS  - CHARACTER*1.
             On entry, TRANS specifies the equations to be solved as
             follows:

                TRANS = 'N' or 'n'   A*x = b.

                TRANS = 'T' or 't'   A'*x = b.

                TRANS = 'C' or 'c'   A'*x = b.

             Unchanged on exit.

    DIAG   - CHARACTER*1.
             On entry, DIAG specifies whether or not A is unit
             triangular as follows:

                DIAG = 'U' or 'u'   A is assumed to be unit triangular.

                DIAG = 'N' or 'n'   A is not assumed to be unit
                                    triangular.

             Unchanged on exit.

    N      - INTEGER.
             On entry, N specifies the order of the matrix A.
             N must be at least zero.
             Unchanged on exit.

    A      - DOUBLE PRECISION array of DIMENSION ( LDA, n ).
             Before entry with  UPLO = 'U' or 'u', the leading n by n
             upper triangular part of the array A must contain the upper

             triangular matrix and the strictly lower triangular part of

             A is not referenced.
             Before entry with UPLO = 'L' or 'l', the leading n by n
             lower triangular part of the array A must contain the lower

             triangular matrix and the strictly upper triangular part of

             A is not referenced.
             Note that when  DIAG = 'U' or 'u', the diagonal elements of

             A are not referenced either, but are assumed to be unity.
             Unchanged on exit.

    LDA    - INTEGER.
             On entry, LDA specifies the first dimension of A as declared

             in the calling (sub) program. LDA must be at least
             max( 1, n ).
             Unchanged on exit.

    X      - DOUBLE PRECISION array of dimension at least
             ( 1 + ( n - 1 )*abs( INCX ) ).
             Before entry, the incremented array X must contain the n
             element right-hand side vector b. On exit, X is overwritten

             with the solution vector x.

    INCX   - INTEGER.
             On entry, INCX specifies the increment for the elements of
             X. INCX must not be zero.
             Unchanged on exit.


    Level 2 Blas routine.

    -- Written on 22-October-1986.
       Jack Dongarra, Argonne National Lab.
       Jeremy Du Croz, Nag Central Office.
       Sven Hammarling, Nag Central Office.
       Richard Hanson, Sandia National Labs.



       Test the input parameters.


   Parameter adjustments
       Function Body */
#define X(I) x[(I)-1]

#define A(I,J) a[(I)-1 + ((J)-1)* ( *lda)]

    info = 0;
    if (! lsame_(uplo, "U") && ! lsame_(uplo, "L")) {
	info = 1;
    } else if (! lsame_(trans, "N") && ! lsame_(trans, "T") &&
	     ! lsame_(trans, "C")) {
	info = 2;
    } else if (! lsame_(diag, "U") && ! lsame_(diag, "N")) {
	info = 3;
    } else if (*n < 0) {
	info = 4;
    } else if (*lda < max(1,*n)) {
	info = 6;
    } else if (*incx == 0) {
	info = 8;
    }
    if (info != 0) {
	xerbla_("DTRSV ", &info);
	return 0;
    }

/*     Quick return if possible. */

    if (*n == 0) {
	return 0;
    }

    nounit = lsame_(diag, "N");

/*     Set up the start point in X if the increment is not unity. This
       will be  ( N - 1 )*INCX  too small for descending loops. */

    if (*incx <= 0) {
	kx = 1 - (*n - 1) * *incx;
    } else if (*incx != 1) {
	kx = 1;
    }

/*     Start the operations. In this version the elements of A are
       accessed sequentially with one pass through A. */

    if (lsame_(trans, "N")) {

/*        Form  x := inv( A )*x. */

	if (lsame_(uplo, "U")) {
	    if (*incx == 1) {
		for (j = *n; j >= 1; --j) {
		    if (X(j) != 0.) {
			if (nounit) {
			    X(j) /= A(j,j);
			}
			temp = X(j);
			for (i = j - 1; i >= 1; --i) {
			    X(i) -= temp * A(i,j);
/* L10: */
			}
		    }
/* L20: */
		}
	    } else {
		jx = kx + (*n - 1) * *incx;
		for (j = *n; j >= 1; --j) {
		    if (X(jx) != 0.) {
			if (nounit) {
			    X(jx) /= A(j,j);
			}
			temp = X(jx);
			ix = jx;
			for (i = j - 1; i >= 1; --i) {
			    ix -= *incx;
			    X(ix) -= temp * A(i,j);
/* L30: */
			}
		    }
		    jx -= *incx;
/* L40: */
		}
	    }
	} else {
	    if (*incx == 1) {
		for (j = 1; j <= *n; ++j) {
		    if (X(j) != 0.) {
			if (nounit) {
			    X(j) /= A(j,j);
			}
			temp = X(j);
			for (i = j + 1; i <= *n; ++i) {
			    X(i) -= temp * A(i,j);
/* L50: */
			}
		    }
/* L60: */
		}
	    } else {
		jx = kx;
		for (j = 1; j <= *n; ++j) {
		    if (X(jx) != 0.) {
			if (nounit) {
			    X(jx) /= A(j,j);
			}
			temp = X(jx);
			ix = jx;
			for (i = j + 1; i <= *n; ++i) {
			    ix += *incx;
			    X(ix) -= temp * A(i,j);
/* L70: */
			}
		    }
		    jx += *incx;
/* L80: */
		}
	    }
	}
    } else {

/*        Form  x := inv( A' )*x. */

	if (lsame_(uplo, "U")) {
	    if (*incx == 1) {
		for (j = 1; j <= *n; ++j) {
		    temp = X(j);
		    for (i = 1; i <= j-1; ++i) {
			temp -= A(i,j) * X(i);
/* L90: */
		    }
		    if (nounit) {
			temp /= A(j,j);
		    }
		    X(j) = temp;
/* L100: */
		}
	    } else {
		jx = kx;
		for (j = 1; j <= *n; ++j) {
		    temp = X(jx);
		    ix = kx;
		    for (i = 1; i <= j-1; ++i) {
			temp -= A(i,j) * X(ix);
			ix += *incx;
/* L110: */
		    }
		    if (nounit) {
			temp /= A(j,j);
		    }
		    X(jx) = temp;
		    jx += *incx;
/* L120: */
		}
	    }
	} else {
	    if (*incx == 1) {
		for (j = *n; j >= 1; --j) {
		    temp = X(j);
		    for (i = *n; i >= j+1; --i) {
			temp -= A(i,j) * X(i);
/* L130: */
		    }
		    if (nounit) {
			temp /= A(j,j);
		    }
		    X(j) = temp;
/* L140: */
		}
	    } else {
		kx += (*n - 1) * *incx;
		jx = kx;
		for (j = *n; j >= 1; --j) {
		    temp = X(jx);
		    ix = kx;
		    for (i = *n; i >= j+1; --i) {
			temp -= A(i,j) * X(ix);
			ix -= *incx;
/* L150: */
		    }
		    if (nounit) {
			temp /= A(j,j);
		    }
		    X(jx) = temp;
		    jx -= *incx;
/* L160: */
		}
	    }
	}
    }

    return 0;

/*     End of DTRSV . */

} /* dtrsv_ */

#ifdef __cplusplus
}
#endif
